The assembly and maintenance of extracellular matrix (ECM) is essential for the normal development, structure, and function of tissues. Problems in cell-ECM interactions resulting from abnormalities in ECM structure are associated with a wide range of disease states and such structural problems can be associated with both the interstitial matrix (IM) and/or the basal lamina (basement membranes, BM). Correlations between abnormalities in the structure of ECM and subsequent disease states are especially well characterized for the glomerular basement membrane (GBM) of the glomerular capillary wall. In this Program Project Grant application, three of the investigators will study the assembly and maintenance of GBM using biochemical approaches and murine transgenic models. Because from an evolutionary standpoint, cell-ECM interactions are fundamental to normal tissue morphology and function; our laboratory utilizes two animal models that allow us to use a reductionalist approach to study these problems in more simplified systems. These models include the invertebrate hydra and the vertebrate, Zebrafish. Hydra belongs to the second oldest Phylum of the animal kingdom and is utilized as our main model because 1) similar to the glomerular filtration unit, its body wall is structurally simplified to a cell bilayer (ectoderm and endoderm) with an intervening ECM that has a similar composition to vertebrate matrices and 2) its high regenerative capacity allows for a wide variety of cellular and molecular approaches to be applied to questions related to cell-ECM interactions. Zebrafish is utilized as a supplementary model because of 1) its rapid embryo genesis (almost all organ systems develop by 48-72 hours post-fertilization) 2) the spectrum of cellular, molecular, and transgenic approaches available with the organism, and 3) it will serve as a translational system that will allow us to rapidly test what we learn from the invertebrate hydra in a vertebrate animal. Therefore, using both models we will analyze the underlying mechanisms of ECM assembly and turnover and test the central hypothesis that, "In specialized tissues organized as a cell bilayer with an intervening ECM, matrix assembly and turnover involves coordinated interactions between both tissue layers and between individual components of the matrix."